Do EMPs drop from components?

In other words, does increasing the “Mechanic” skill increase the chance of getting them ?

Since EMP cells (small, medium and large) are part of machine and are considered as machine components, yes, Mechanic skill increases the chances of getting them.

Other EMP weaponry, e.g car battery or EMP rocket, aren’t affected by Mechanic skill. Salvage affects the findings of EMP rockets though.